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<meta name="description" content="TCP（transport control protocol，传输控制协议）是面向连接的，面向流的，提供高可靠性服务。收发两端（客户端和服务器端）都要有一一成对的socket， 因此，发送端为了将多个发往接收端的包，更有效的发到对方，使用了优化方法（Nagle算法），将多次间隔较小且数据量小的数据，合并成一个大的数据块， 然后进行封包。这样，接收端，就难于分辨出来了，必须提供科学的拆包机制。即面向">
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          <h1 class="post-title" itemprop="name headline">TCP粘包处理</h1>
        

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        <p><code>TCP</code>（transport control protocol，<code>传输控制协议</code>）是<code>面向连接</code>的，面向流的，提供高可靠性服务。收发两端（客户端和服务器端）都要有一一成对的socket，</p>
<p>因此，发送端为了将多个发往接收端的包，更有效的发到对方，使用了优化方法（<code>Nagle算法</code>），将多次间隔较小且数据量小的数据，合<code>并成一个大的数据块</code>，</p>
<p>然后进行<code>封包</code>。这样，接收端，就难于分辨出来了，必须提供科学的拆包机制。即面向流的通信是无消息保护边界的。</p>
<p><code>UDP</code>（user datagram protocol，用户数据报协议）是<code>无连接的</code>，<code>面向消息</code>的，提供高效率服务。不会使用块的合并优化算法，</p>
<p>由于UDP支持的是一对多的模式，所以接收端的<code>skbuff(套接字缓冲区）</code>采用了链式结构来记录每一个到达的UDP包，</p>
<p>在每个UDP包中就有了消息头（消息来源地址，端口等信息），这样，对于接收端来说，就容易进行区分处理了。 即<code>面向消息的通信是有消息保护边界的</code>。<br><a id="more"></a></p>
<h2 id="TCP粘包我总结了几种情况"><a href="#TCP粘包我总结了几种情况" class="headerlink" title="TCP粘包我总结了几种情况"></a>TCP粘包我总结了几种情况</h2><p><img src="cpptcpnian/1.png" alt="1.png"><br>tcp发送端发送三个包过来，tcp接收缓存区收到了这三个包，而用户的读写缓存区比这三个包的总大小还大，</p>
<p>此时数据是接受完全的，用户缓存区读到三个包需要分开，这是比较好处理的。<br><img src="cpptcpnian/2.png" alt="2.png"><br>第二种情况是因为用户的接收缓存区比tcp接受缓存区大，或者比tcp目前接收到的总数据大，那么用户缓存区读到</p>
<p>的数据就是tcp接收缓存区的数据，这是第一种情况的特例，这种情况需要判断那些包接受完全，那些包没接受完全。<br><img src="cpptcpnian/3.png" alt="3.png"><br>第三种情况是用户的接受缓存区比tcp接受缓存区要小，导致用户缓存区读到的数据是tcp接收缓存区</p>
<p>的一部分，这其中有完整的包，也有残缺的包。<br><img src="cpptcpnian/4.png" alt="4.png"><br>第四种情况是第三种情况的一个特例，用户缓存区的数据是不完全的，只是tcp缓存区的一部分。</p>
<p>对应特别大的那种包。</p>
<p>我提倡的解决办法就是首先实现一套从tcp缓存区中读取数据的数据结构和算法，因为tcp是面向</p>
<p>字节流的，将tcp缓存区中的数据读到用户缓存区里，这里我简单叫做outstreambuffer和instreambuffer，</p>
<p>这两个结构一个用于向tcp写，一个用于从tcp读。把tcp缓存区的数据尽可能多的读出来，不要判断是否是</p>
<p>完整的包，保证tcp缓存区没数据，这样会减少tcp粘包几率。</p>
<p>第二部就是将读到的数据，也就是instreambuffer中的数据进行分割，我叫做切包，切出一个个完整的包，</p>
<p>剩余不完整的留着下次继续接收。</p>
<p>第三步服务器应用层接口从instreambuffer中读取切割好的完整的包进行逻辑处理。</p>
<p>所以为了处理粘包和切包，需要我们自己设计包头，我设计的包头是八字节的结构体，</p>
<p>包含四字节的包id和四字节的包长度，这个长度既可以表示包头+消息体的长度，</p>
<p>也可以表示后面消息体的长度。我设计的是表示后面消息体的长度。</p>
<p>而上面所说的instreambuffer和outstreambuffer用户可以自己设计实现，也可以</p>
<p>利用成熟的网络库，我用的是libevent中的bufferevent，bufferevent实现了类似</p>
<p>的instreambuffer和outstreambuffer。</p>
<p>我设计的服务器部分代码如下，感兴趣可以去git下载：</p>
<p><a href="https://github.com/secondtonone1/smartserver" target="_blank" rel="noopener">https://github.com/secondtonone1/smartserver</a></p>
<p>简单列举下接收端处理读数据的过程。<br><figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">void</span> NetWorkSystem::tcpread_cb(struct bufferevent *bev, <span class="keyword">void</span> *ctx)</span><br><span class="line">&#123;</span><br><span class="line">    getSingleton().dealReadEvent(bev, ctx);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>networksystem是单例模式，处理读事件。因为静态函数tcpread_cb是libevent</p>
<p>设计格式的回调处理函数，在静态函数中调用非静态函数，我采用了单例调用。</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">void</span> NetWorkSystem::dealReadEvent(struct bufferevent *bev, <span class="keyword">void</span> *ctx)</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//</span></span><br><span class="line">    <span class="keyword">evutil_socket_t</span>  bufferfd = bufferevent_getfd(bev);</span><br><span class="line">    <span class="built_in">std</span>::<span class="built_in">map</span>&lt;<span class="keyword">evutil_socket_t</span>, TcpHandler *&gt;::iterator tcpHandlerIter = m_mapTcpHandlers.find(bufferfd);</span><br><span class="line">    <span class="keyword">if</span>(tcpHandlerIter != m_mapTcpHandlers.end())</span><br><span class="line">    &#123;</span><br><span class="line">        tcpHandlerIter-&gt;second-&gt;dealReadEvent();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>tcphandler是我设计的切包类，这里通过bufferfd找到对应的instream和outstream，从而处理里面的数据完成切包。<br><figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//处理读事件</span></span><br><span class="line"><span class="keyword">void</span> TcpHandler::dealReadEvent()</span><br><span class="line">&#123;</span><br><span class="line">    evbuffer * inputBuf = bufferevent_get_input(m_pBufferevent);</span><br><span class="line">    <span class="keyword">size_t</span> inputLen = evbuffer_get_length(inputBuf);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">while</span>(inputLen &gt; <span class="number">0</span>)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="comment">//tcphandler第一次接收消息或者该node接收完消息，需要开辟新的node接受消息</span></span><br><span class="line">        <span class="keyword">if</span>(!m_pLastNode || m_pLastNode-&gt;m_nMsgLen &lt;= m_pLastNode-&gt;m_nOffSet)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="comment">//判断消息长度是否满足包头大小，不满足跳出</span></span><br><span class="line">            <span class="keyword">if</span>(inputLen  &lt; PACKETHEADLEN)</span><br><span class="line">            &#123;</span><br><span class="line">                <span class="keyword">break</span>;</span><br><span class="line">            &#125;</span><br><span class="line"></span><br><span class="line">            <span class="keyword">char</span> data[PACKETHEADLEN]  = &#123;<span class="number">0</span>&#125;;</span><br><span class="line">            bufferevent_read(m_pBufferevent, data, PACKETHEADLEN);</span><br><span class="line">            <span class="class"><span class="keyword">struct</span> <span class="title">PacketHead</span>  <span class="title">packetHead</span>;</span></span><br><span class="line"></span><br><span class="line">            <span class="built_in">memcpy</span>(&amp;packetHead, data, PACKETHEADLEN);</span><br><span class="line"></span><br><span class="line">            <span class="built_in">cout</span> &lt;&lt; <span class="string">"packetId is : "</span> &lt;&lt;packetHead.packetID &lt;&lt; <span class="built_in">endl</span>;</span><br><span class="line"></span><br><span class="line">            <span class="built_in">cout</span> &lt;&lt; <span class="string">"packetLen is :  "</span> &lt;&lt; packetHead.packetLen &lt;&lt; <span class="built_in">endl</span>;</span><br><span class="line"></span><br><span class="line">            insertNode(packetHead.packetID, packetHead.packetLen);</span><br><span class="line"></span><br><span class="line">            inputLen -= PACKETHEADLEN;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="comment">//考虑可能去包头后剩余的为0</span></span><br><span class="line">        <span class="keyword">if</span>(inputLen &lt;= <span class="number">0</span>)</span><br><span class="line">        &#123;</span><br><span class="line">            <span class="keyword">break</span>;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//读取去除包头后剩余消息</span></span><br><span class="line">        tcpRead(inputLen);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>这个函数判断是否读完一个消息，读完就开辟新的节点存储新来的消息，否则就将新来的消息放入没读完的节点里。<br><figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">void</span> TcpHandler::tcpRead(UInt32 &amp;inputLen)</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//node节点中的数据还有多少没读完</span></span><br><span class="line">    UInt32 remainLen = m_pLastNode-&gt;m_nMsgLen - m_pLastNode-&gt;m_nOffSet;</span><br><span class="line"></span><br><span class="line">    UInt32 readLen = bufferevent_read(m_pBufferevent, m_pLastNode-&gt;m_pMsg + m_pLastNode-&gt;m_nOffSet, remainLen);</span><br><span class="line">    <span class="comment">//统计bufferevent 的inputbuffer中剩余的长度</span></span><br><span class="line">    inputLen -= readLen;</span><br><span class="line">    <span class="comment">//更改偏移标记</span></span><br><span class="line">    m_pLastNode-&gt;m_nOffSet += readLen;</span><br><span class="line">    <span class="comment">//判断读完</span></span><br><span class="line">    <span class="keyword">if</span>(m_pLastNode-&gt;m_nOffSet &gt;= m_pLastNode-&gt;m_nMsgLen)</span><br><span class="line">    &#123;</span><br><span class="line">        m_pLastNode-&gt;m_pMsg[m_pLastNode-&gt;m_nMsgLen + <span class="number">1</span>] = <span class="string">'\0'</span>; </span><br><span class="line">        <span class="built_in">cout</span> &lt;&lt; <span class="string">"receive msg is : "</span> &lt;&lt; m_pLastNode-&gt;m_pMsg &lt;&lt; <span class="built_in">endl</span>;</span><br><span class="line">        <span class="comment">//cout &lt;&lt;"read times is :  " &lt;&lt; ++readtimes&lt;&lt; endl;</span></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>我的服务器还在完善中，目前已经能处理连续收到1万个包的切包和大并发的问题了，最近在设计应用层的序列化</p>
<p>和应用层消息回调。感兴趣可以下载看看，下载地址：<a href="https://github.com/secondtonone1/smartserver" target="_blank" rel="noopener">https://github.com/secondtonone1/smartserver</a></p>

      
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                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  
  

  

  

  

</body>
</html>
